Variable dispersion of wet use chopped strand glass fibers in a chopped title strand mat

ABSTRACT

A size composition for reinforcement fibers used to form non-woven mats that contain variable amounts of individual filaments dispersed from chopped reinforcement fiber bundles is provided. The size composition contains a polyvinylamine film former, one or more silane coupling agents, and, optionally a lubricant. The size composition works in conjunction with the whitewater components in a wet-laid mat forming process to disperse individual filaments from the bundles of chopped fibers. The whitewater contains an anionic polyacrylamide viscosity modifier and/or a cationic or non-ionic amine dispersant (e.g., ethoxylated amine). The presence of a cationic or non-ionic amine in the whitewater disperses individual filaments from the chopped glass fiber bundles. The greater the amount of cationic or non-ionic amine present in the whitewater, the greater the amount of fiber dispersion. The absence of a cationic or non-ionic amine and the presence of an anionic polyacrylamide viscosity modifier maintain full bundle formation integrity.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to size compositions for glass fibers, and more particularly, to a size chemistry that works in conjunction with whitewater chemistry to variably disperse filaments from bundles of chopped reinforcement fibers in the whitewater of wet-laid mat forming applications.

BACKGROUND OF THE INVENTION

Typically, glass fibers are formed by drawing molten glass into filaments through a bushing or orifice plate and applying an aqueous sizing composition containing lubricants, coupling agents, and film-forming binder resins to the filaments. The sizing composition provides protection to the fibers from interfilament abrasion and promotes compatibility between the glass fibers and the matrix in which the glass fibers are to be used. After the sizing composition is applied, the wet fibers may be gathered into one or more strands, chopped, and collected. The chopped strands may contain hundreds or thousands of individual glass fibers. The collected chopped glass strands may then be packaged in their wet condition as wet chopped fiber strands (WUCS) or dried to form dry chopped fiber strands (DUCS).

Wet chopped fibers are conventionally used in wet-laid processes in which the wet chopped fibers are dispersed in a water slurry that contains surfactants, viscosity modifiers, defoaming agents, and/or other chemical agents (e.g., whitewater). The slurry containing the chopped fibers is agitated so that the fibers become dispersed throughout the slurry. The slurry containing the fibers is deposited onto a moving screen where a substantial portion of the water is removed to form a web. A binder is then applied, and the resulting mat is dried to remove any remaining water and cure the binder. The formed non-woven mat is an assembly of dispersed, individual glass filaments.

Fibrous mats formed by wet-laid processes are extremely suitable as reinforcements for many types of applications. For example, wet-laid mats may be used in roofing applications, non-woven veil applications, or to form composite laminates or ceiling tiles. Because the fibers are not dried prior to use, wet-laid mats provide a lower cost alternative to dry-laid mats. Besides their economic advantage, wet-laid mats have the attributes of good wettability for impregnation by plastic resins, quick air releasing capacity, and superior surface characteristics. In addition, they serve well as spacing and core material.

Despite these many desirable attributes, attempts are continually being made to improve conventional chopped strand mats. One particular area of interest is improving the tear and tensile strengths of the mats, as these properties are consumer-oriented and consumer-driven. Conventionally, the wet chopped fibers are designed to disperse well in the whitewater. However, in order for the final glass reinforced product to achieve acceptable mechanical performance, it must include a sufficient amount by weight of glass reinforcements. Accordingly, it is desirable to increase the glass fiber content in conventional wet-laid chopped strand mats. Some examples of attempts to improve chopped strand mats are set forth below.

U.S. Pat. Nos. 4,112,174 and 4,129,674 to Hannes et al. disclose glass mats that are formed of a web of monofilament fibers and elongated glass fiber bundles preferably contain about 20-300 monofilaments. The fibrous mats are formed by wet-laid processes. The bundles are coated with a water or another liquid insoluble binder. To keep the glass fiber bundles in a bundle form in the slurry during the mat forming process.

U.S. Pat. Nos. 4,200,487 and 4,242,404 to Bodoc et al. describe glass mats that include individual glass filaments and extended glass fiber elements. The extended glass fiber elements are formed from bundles of glass fibers that slide apart and become connected longitudinally when the whitewater slurry is agitated. It is asserted that the glass fiber elements contribute to high strength properties of the mat and that the individual filaments provide a uniform denseness necessary for the impregnation of asphalt in the manufacturing of roofing shingles. The mats are formed by a wet-laid process.

U.S. Pat. No. 6,187,697 to Jaffee et al. describes a two layer fibrous mat formed of (1) a body portion layer and (2) a surface portion layer that includes fine fibers and/or particles. The layers are bonded together with a resin binder. Preferably, most of the particles and/or fibers in the surface layer are larger than the openings between the fibers in the body portion of the mat. The mats are made on a wet laid non-woven mat machine.

U.S. Pat. No. 6,767,851 and U.S. Patent Application Publication No. 2002/0092634 to Rokman et al. disclose non-woven mats in which at least 20% of the fibers are present as fiber bundles having about 5-450 fibers per bundle. In preferred embodiments, at least 85% of the fibers in the mats are in the form of bundles. The fibers are held in the bundles by a substantially non-water soluble sizing such as an epoxy resin or PVOH. The bundles may comprise at least 10% reinforcing fibers such as glass fibers. The mat may be made by a foam or water process.

U.S. Patent Publication No. 2005/0022956 to Rodriguez, et al. teaches a composition for surface sizing and strengthening paper and other cellulosic products. The composition is an aqueous mixture of a film forming binder, an anionic polymer, and a cationic polymer. Examples of suitable cationic polymers include polyamines, polyethylene amines, acrylamide, and methacrylamide. The film forming binder may be a polysaccharide or derivatives thereof, or synthetic polymers, particularly vinyl polymers such as polyvinylamine.

Although conventional wet-laid mats are continually being improved, there remains a need in the art for a method for improving the tear strength of chopped strand mats, especially during the manufacture of the chopped strand mats.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a sizing composition that is formed of a polyvinylamine film former, one or more silane coupling agents, and optionally a lubricant. The film formers may be divided into groups including low molecular weight (e.g., 10³-10⁴ g/mol), medium molecular weight (e.g., 10⁴-10⁵ g/mol), and high molecular weight (e.g., 10⁵-10⁶ g/mol). A weak acid such as acetic acid may be added to the size composition to assist in the hydrolysis of the silane coupling agent and/or to bring the pH of the size composition to between 4.5 and 6. The sizing composition may optionally contain conventional additives such as antifoaming agents, antistatic agents, and/or thickening agents. The size composition is applied to any type of organic, inorganic, or natural fiber suitable for providing good structural qualities and durability. Preferably, the fibers are glass fibers. The size composition may be applied to the reinforcing fibers in an amount sufficient to achieve a strand solids content from about 0.05 to about 1.0% and/or a forming moisture from about 5.0 to about 20.0%. The size on the glass reinforcement fibers (1) maintains bundle integrity when the bundles are added to the whitewater and agitated during a wet-laid process and (2) at least partially disperses individual reinforcement fibers from the fiber bundles. The size composition works in conjunction with the whitewater components in a wet-laid mat forming process to form non-woven mats that contain variable amounts of filaments that are dispersed from the chopped reinforcement fiber bundles.

It is also an object of the present invention to provide a wet-laid chopped strand mat that may be formed of bundles of fibers or a combination of fiber bundles and individual fibers. Reinforcing fibers suitable for use in the chopped strand mat include glass fibers, wool glass fibers, natural fibers, mineral fibers, carbon fibers, and ceramic fibers. The reinforcing fibers are at least partially coated with a size composition that contains a polyvinylamine film former and at least one silane coupling agent. The size composition for reinforcement fibers works in conjunction with the whitewater components in a wet-laid mat forming process to obtain non-woven mats that contain variable amounts of filaments dispersed from the chopped reinforcement fiber bundles. In some exemplary embodiments, all of the reinforcement fibers remain in a bundled form and form a mat similar to a mat formed by a dry-laid mat forming process. In other exemplary embodiments, chopped strand mats are formed that contain bundles of reinforcing fibers and discrete (e.g., individual) reinforcing fibers dispersed or released from the fiber bundles. The degree of bundle integrity is dependent on the final application for the chopped strand mat. In other words, the specific number of fibers present in the reinforcing fiber bundles will vary depending on the particular application of the chopped strand mat and the desired strength and thickness of the mat. It is preferred that the reinforcing fiber bundles have a bundle tex from 20-250 g/km.

It is also an object of the present invention to provide a method of forming a chopped strand mat. Chopped reinforcement fiber bundles (e.g., glass fiber bundles) are placed into a mixing tank that contains whitewater formed of an anionic polyacrylamide viscosity modifier and/or a cationic or non-ionic amine dispersant such as an ethoxylated amine dispersant. The chopped glass bundles are mixed with agitation to form a chopped glass fiber bundle slurry. The slurry may be passed through a machine chest and a constant level chest to further disperse any fibers selectively released from the chopped glass fiber bundles by the interaction of the size composition and any cationic or non-ionic amine dispersant (e.g., ethoxylated amine dispersant) present in the whitewater. The glass fiber bundle slurry may then be transferred onto a moving screen or foraminous conveyor and a substantial portion of the water from the slurry is removed to form a web. The water may be removed from the web by a conventional vacuum or air suction system. A binder is then applied to the web and the binder-coated web is passed through a drying apparatus such as a drying oven to remove any remaining water and cure the binder. The chopped strand mat may be formed of 0-100% by weight (based on the total fibers) of reinforcement fiber bundles and from 0-100% by weight (based on the total fibers) of individual reinforcement fibers. The inventive size composition works with the components of the whitewater to selectively disperse the filaments from the bundles. In particular, if no cationic or non-ionic amine dispersant is present in the whitewater, the size chemistry works with the anionic polyacrylamide thickener to maintain the bundled formation of the fibers. The size works with the cationic or non-ionic amine dispersant (e.g., ethoxylated amine dispersant) to release fibers from the fiber bundles.

It is an advantage of the present invention that the chopped strand mat can be engineered or controlled to have a predetermined amount of reinforcement fiber bundles and individual reinforcement fibers.

It is another advantage of the present invention that by adjusting the permeability or degree of dispersion in the white water, the mat can be engineered to allow for the introduction of various fillers.

It is yet another advantage of the present invention that the increased laminate glass content that is imparted by the chopped strand mats relative to a traditional wet-laid mat provides improved mechanical and impact performance in the final composite products.

It is another advantage of the present invention that the chopped glass fiber bundles can be formed with low manufacturing costs since the wet glass fibers are chopped in-line and not dried until processed as a glass mat.

It is a further advantage of the present invention that the retention of fiber bundles allows for the chopped strand mat to have a higher glass content per volume than conventional wet-laid dispersed fiber mats.

It is a feature of the present invention that the degree of dispersion of filaments from the reinforcement fiber bundles is controlled by the concentration of the thickener and dispersant present in the whitewater.

It is another feature of the present invention that the final morphology of the chopped strand mat can be adjusted to provide ranges of dispersion of the filaments from the fiber bundles in the chopped strand mat.

It is yet another feature of the present invention that a bundled fiber preform can be made with wet glass fibers.

The foregoing and other objects, features, and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description that follows. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a processing line for forming a chopped strand mat according to one exemplary embodiment of the present invention;

FIG. 2 is an enlarged partial perspective view of a chopped glass fiber mat formed of bundles of glass fibers and individual glass fibers according to at least one exemplary embodiment of the present invention;

FIG. 3 is a photographic illustration of a preform containing fully retained glass fiber bundles according to one exemplary embodiment of the present invention;

FIG. 4 is a photographic illustration of a preform containing partially dispersed glass fiber bundles according to one exemplary embodiment of the present invention; and

FIG. 5 is a graphical illustration of the normalized tensile strengths of molded preform laminates.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references.

In the drawings, the thickness of the lines, layers, and regions may be exaggerated for clarity. It is to be noted that like numbers found throughout the figures denote like elements. Terms such as “top”, “bottom”, “side”, “upper”, “lower” and the like are used herein for the purpose of explanation only. It will be understood that when an element is referred to as being “on,” another element, it can be directly on or against the other element or intervening elements may be present. The terms “sizing”, “size”, “sizing composition”, “size composition”, and “size chemistry” may be interchangeably used herein. The terms “strand” and “bundle” may also be used interchangeably herein. In addition, the terms “fiber” and “filament” may be interchangeably used in this application. Further, the terms “bundle” and “strand” may be interchangeably used herein.

The present invention relates to a size composition for reinforcement fibers that works in conjunction with whitewater components in a wet-laid mat forming process to obtain non-woven mats that contain variable amounts of filaments that are dispersed from chopped reinforcement fiber bundles. The amount of individual filaments that are dispersed from the reinforcement bundles may also be controlled by the forming conditions of the reinforcing fibers, such as the strand solids and forming moisture. In some exemplary embodiments, all of the reinforcement fibers remain in a bundled form and form a mat similar to a mat formed by a dry-laid mat forming process. In other exemplary embodiments, chopped strand mats are formed that contain bundles of reinforcing fibers and discrete (e.g., individual) reinforcing fibers that have been released from the reinforcing fiber bundles. The degree of bundle integrity or fiber dispersion is dependent on the final application for the chopped strand mat.

The reinforcing fibers forming the chopped strand mat may be any type of organic, inorganic, or natural fiber suitable for providing good structural qualities and durability. Examples of suitable reinforcing fibers include glass fibers, wool glass fibers, natural fibers, mineral fibers, carbon fibers, and ceramic fibers. The term “natural fiber” as used in conjunction with the present invention refers to plant fibers extracted from any part of a plant, including, but not limited to, the stem, seeds, leaves, roots, or bast. The reinforcing fibers forming the chopped strand mat may include only one type of reinforcement fiber (such as glass fibers) or, alternatively, more than one type of reinforcement fiber may be used in forming the chopped strand mat. The inclusion of synthetic fibers or polymer resins such as polyester, polyethylene, polyethylene terephthalate, polypropylene, and/or polyparaphenylene terephthalainide (sold commercially as Kevlar®) in the chopped strand mat is considered to be within the purview of the invention. The addition of a synthetic fiber or polymer resin may enhance the tensile strength of the mat. Additionally, the use of synthetic fibers may act as a mat binder in later processing to assist in holding the chopped fiber bundles together when forming a chopped strand mat.

In preferred embodiments, all of the reinforcing fibers are glass fibers. Any type of glass fiber, such as A-type glass fibers, C-type glass fibers, E-type glass fibers, S-type glass fibers, AR-type glass, ECR-type glass fibers (e.g., Advantex® glass fibers commercially available from Owens Corning), or modifications thereof may be used as the reinforcing fibers. In at least one preferred embodiment, the reinforcing fibers are wet use chopped strand glass fibers (WUCS). Wet use chopped strand glass fibers for use as the reinforcement fibers may be formed by conventional processes known in the art. It is desirable that the wet use chopped strand glass fibers have a moisture content from about 5 to about 30%, and even more desirably a moisture content from about 5 to about 15%. In addition, the presence of reinforcement fibers improves the wet strength of the mat prior to curing the binder.

The reinforcing fibers may be chopped fibers having a length of approximately 0.25 to about 2 inches, and preferably a length from about 0.75 to about 1.5 inches. In addition, the reinforcing fibers may have diameters from about 7 to about 20 microns, and preferably from about 10 to about 16 microns. Additionally, the reinforcing fibers may have varying lengths and diameters from each other within the chopped strand mat. The reinforcement fibers may be present in the chopped strand mat, in the form of bundles (i.e., strands) and individual fibers in an amount from approximately 0-99% by weight of the final product.

The non-woven chopped strand mat may be formed by the wet-laid process described below. It is to be noted that the exemplary process is described herein with respect to a preferred embodiment in which the reinforcement fibers are glass fibers. As is known in the art, glass fibers may be formed by attenuating streams of a molten glass material from a bushing or orifice. An aqueous sizing composition is applied to the fibers after they are drawn from the bushing. The sizing may be applied, for example, by application rollers or by spraying the size directly onto the fibers. Generally, the size protects the fibers from breakage during subsequent processing, helps to retard interfilament abrasion, ensures the integrity of the strands of glass fibers, e.g., the interconnection of the glass filaments that form the strand, and potentially improves compatibility between the resin matrix and the glass fibers.

In the present invention, the size on the glass fibers also maintains bundle integrity when the bundles are added to the whitewater and agitated in a wet-laid process as described below. The inventive size composition is formed of a polyvinylamine film former to hold the glass fibers in bundles, one or more silane coupling agents to bond the glass fibers to the resin matrix, and optionally a lubricant to assist in reducing fiber-to-fiber abrasion. A weak acid such as acetic acid, boric acid, metaboric acid, succinic acid, citric acid, formic acid, and/or polymeric acids such as polyacrylic acids may be added to the size composition to assist in the hydrolysis of the silane coupling agent and/or to bring the pH of the size composition to between 4.5 and 6. The size composition may be applied to the fibers in an amount sufficient to achieve a strand solids content from about 0.05 to about 1.0% and/or a forming moisture from about 5.0 to about 20.0%.

Non-limiting examples of suitable polyvinylamine film formers include Lupamin 1595, Lupamin 5095, and Lupamin 9095 (all of which are commercially available from BASF). The film former may be present in the size composition in an amount from about 80 to about 95% by weight of the total composition, and preferably in an amount from about 85 to about 92% by weight. The polyvinylamine film former has a molecular weight ranging from about 10³ g/mol to about 10⁶ g/mol. For ease of discussion in this application, the film formers may be divided into a low molecular weight (i.e., 10³-10⁴ g/mol), a medium molecular weight (i.e., 10⁴-10⁵ g/mol), and a high molecular weight (i.e., 10⁵-10⁶ g/mol).

As discussed above, the size composition includes one or more silane coupling agents. Silane coupling agents enhance the adhesion of the film former to the glass fibers and reduce the level of fuzz, or broken fiber filaments, during subsequent processing. Examples of silane coupling agents which may be used in the present size composition may be characterized by the functional groups amino, epoxy, vinyl, methacryloxy, ureido, and isocyanato. Suitable coupling agents for use in the size composition are available commercially, such as, for example, γ-aminopropyltriethoxysilane (A-1100), methacryloxypropyltriethoxysilane (A-174), β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (A-186), γ-glycidoxypropyltrimethoxysilane (A-187), n-trimethoxy-silyl-propyl-ethylene-diamine (A-1120), and vinyl-triacetoxy silane (A-188), all of which are commercially available from Momentive Materials. Preferably, the coupling agent is an epoxy silane, such as γ-glycidoxypropyltrimethoxysilane (A-187 from Momentive Materials). The silane coupling agent is present in the size composition in an amount from about 5.0 to about 20.0% by weight of the total composition, and even more preferably, in an amount from about 7 to about 13% by weight of the total composition.

In addition, the size composition may include at least one lubricant to facilitate manufacturing. The lubricant may be present in the size composition in an amount from about 0.5 to about 5% by weight of the total composition. Any suitable lubricant may be used. Lubricants suitable for use in the size composition include, but are not limited to, partially amidated long-chain polyalkylene imines such as Emery 6760L (Cognis), ethyleneglycol oleates, ethoxylated fatty amines, glycerine, emulsified mineral oils, organopolysiloxane emulsions, stearic ethanolamide, sold under the trade designation Lubesize K-12 (available from AOC), PEG 400 MO (or MS), a monooleate (or monostearate) ester having about 400 ethylene oxide groups (available from Cognis), and Lonzest SMS-20, a sorbitan monostearate ester having about 20 ethylene oxide groups (available from Lonza).

The sizing composition utilized may optionally contain conventional additives such as, but not limited to, antifoaming agents such as Drew L-139 (available from Drew Industries, a division of Ashland Chemical), antistatic agents such as Emerstat 6660A (available from Cognis), Surfynol 465 (available from Air Products), Triton X-100 (available from Cognis), and/or thickening agents. Additives may be present in the size composition from trace amounts (such as <0.1% by weight of the total composition) up to approximately 5.0% by weight of the total composition.

After the fibers are treated with the sizing composition, they are collected as bundles of fibers and chopped into discrete lengths. The fiber bundles are formed of a plurality of the chopped glass fibers positioned in a substantially parallel orientation to each other. The specific number of individual fibers present in the glass fiber bundles will vary depending on the particular application of the chopped strand mat and the desired strength and thickness of the mat. The glass fiber bundles may have a bundle tex from 20 g/km to 600 g/km, and preferably from 20 g/km to 200 g/km.

A chopped strand mat according to one exemplary embodiment of the present invention may be formed as depicted in FIG. 1. Chopped glass bundles 10 may be provided to a conveyor 12 by a storage container 14. The chopped glass fiber bundles 10 are placed into a mixing tank 16 that contains whitewater formed of an anionic polyacrylamide viscosity modifier (e.g., Nalco 7768) and/or a cationic or non-ionic amine dispersant such as an ethoxylated amine dispersant (e.g., Nalco 01 nm 159). Optionally, defoaming and/or other chemical agents may be present in the whitewater. The chopped glass bundles 10 are mixed with agitation to form a chopped glass fiber bundle slurry (not shown) that may be formed of bundles of fibers, a combination of bundles of fibers and fibers dispersed from the fiber bundles, or a plurality of individual glass fibers. The slurry may be passed through a machine chest 18 and a constant level chest 20 to further disperse fibers from the chopped glass fiber bundles 10 by the interaction of the size composition and the cationic or non-ionic amine dispersant. The glass fiber bundle slurry may then be transferred from the constant level chest 20 to a head box 22 where the slurry is deposited onto a moving screen or foraminous conveyor 21 and a substantial portion of the water from the slurry is removed to form a web 24. The water may be removed from the web 24 by a conventional vacuum or air suction system (not illustrated in FIG. 1). A binder 26 is then applied to the web 24 by a binder applicator 28. The binder-coated web 30 is then passed through a drying oven 32 to remove any remaining water and cure the binder. The non-woven chopped strand mat 34 may be rolled onto a take-up roll 36 for storage for later use.

The binder 26 may be an acrylic or acrylate binder, a styrene acrylonitrile binder, a styrene butadiene rubber binder, a urea formaldehyde binder, or mixtures thereof. Preferably, the binder is a standard thermosetting acrylic binder formed of polyacrylic acid and at least one polyol (e.g., triethanolamine or glycerin). Examples of suitable binders for use in the present invention include a plasticized polyvinylacetate binder such as Vinamul 8831 (available from Celanese) and modified polyvinylacetates such as Duracet 637 and Duracet 675 (available from Franklin International). The binder may optionally contain conventional additives for the improvement of process and product performance such as dyes, oils, fillers, colorants, UV stabilizers, coupling agents (e.g., aminosilanes), lubricants, wetting agents, surfactants, and/or-antistatic agents.

The chopped strand mat 34 may be formed of 0-100% by weight (based on the total fibers) of reinforcement fiber bundles and from 0-100% by weight (based on the total fibers) of individual reinforcement fibers. The proportional amount of the individual reinforcement fibers (e.g., glass) fibers and reinforcement fiber bundles (e.g., glass fiber bundles) present in the chopped strand mat will vary depending on the desired application of the mat. For example, in an application where there is a minor requirement for surface quality and a higher structural requirement, a very high number of reinforcement fiber bundles (such as ≧95% by weight, based on the total fibers) may be present in the chopped strand mat. In this embodiment, substantially none of the fibers disperse from the fiber bundles in the white water slurry during agitation. The phrase “substantially none” is meant herein to denote that no individual fibers, or nearly no individual fibers, are released from the fiber bundles. For example, and as discussed below, the glass fibers may remain in a bundle throughout the mat forming process. Alternatively, for a less structurally demanding, but more surface conscious component, the chopped strand mat may have a larger amount of individual reinforcement fibers (such as ≧30% by weight, based on the total fibers). A schematic example of a chopped strand mat 40 containing both chopped reinforcement fiber bundles 10 and individual reinforcement fibers 42 is depicted in FIG. 2.

The inventive size composition works with the components of the whitewater to disperse (e.g., selectively disperse) the filaments from the fiber bundles. In particular, the size chemistry works with the anionic polyacrylamide thickener present in the whitewater to maintain the bundled formation of the reinforcement fibers. Although not wishing to be bound by theory, it is believed that the cationic polyvinylamine film former in the size chemistry is attracted to the anionic glass fibers through an ionic interaction. As a result, the cationic polyvinylamine dominates the glass interface and surrounds the individual glass fibers. After the coated fibers are physically gathered into strands, a cationic charge exists around the fiber bundle. When the positively charged fiber bundles are introduced into whitewater that contains an anionic polymeric species, such as the negatively charged polyacrylamide thickening agent, the anionic polymeric species surrounds the fiber bundle in an encapsulating-like manner. This “encapsulation” of the fiber bundles forces the fiber bundles to remain in a bundled form, and may cause the glass fiber bundles to agglomerate with each other.

It is further hypothesized that the “encapsulation” of the fiber bundles by the polyacrylamide thickening agent makes the outside of the fiber bundle negatively charged, like the surrounding medium. It is also speculated that there may not be enough miscibility between the polyvinylamine interphase and the polacrylamide, which may also assist in the retention of the fiber bundles. It is further believed that when the molecular weight of the polyvinylamine film former is high enough, a portion of the polymer is free from ionic interaction with the glass surface, thereby allowing the potential for additional activity during the wet-laid mat forming process.

The cationic or non-ionic amine dispersant (e.g., ethoxylated amine) in the whitewater begins to break up the fiber bundles before the polyvinylamine film former and the polyacrylamide thickening agent completely seal the fiber bundle, which causes the bundles of fibers to disassociate and release individual filaments. Thus, by varying the amount of cationic or non-ionic amine dispersant present in the whitewater, the amount of fibers released from the reinforcement fiber bundles may be varied. Specifically, the greater the amount of cationic or non-ionic amine dispersant (e.g., ethoxylated amine) present in the whitewater, the greater the amount of fibers that are dispersed or released from the chopped fiber bundles. If the whitewater contains a cationic or non-ionic amine dispersant such as an ethoxylated amine dispersant and no anionic polyacrylamide thickener, all or substantially all of the fibers in the fiber bundles will be dispersed into the whitewater. On the other hand, if no cationic or non-ionic amines are present in the whitewater, then all or substantially all of the fibers remain in a bundled formation. It is to be appreciated, however, that a small amount of cationic or non-ionic amine (e.g., ethoxylated amine) in the whitewater (e.g., <50 ppm) will not disrupt the bundled formation of the glass fibers.

The dispersion of the reinforcement fibers from the reinforcement fiber bundles may also be adjusted by changing the strand solids and forming moisture of the reinforcement fibers without altering the sizing composition. For example, the release of the fibers from the fiber bundles may be controlled by regulating the concentration and charge density of the polyacrylamide viscosity modifier. Alternatively, the charge density on the backbone of the fiber can be managed to control the dispersion of the fibers from the fiber bundles. Because the amount of individual reinforcement fibers present in the slurry can be controlled, the chopped strand mat may be fine tuned and/or formed with predetermined amounts of fiber bundles and individual fibers in order to meet the needs of a particular application.

By selectively adjusting the permeability or degree of dispersion of the fibers from the fiber bundles in the white water, the mat can be engineered to allow for the introduction of various fillers, such as calcium carbonate, talc, and/or other well-known mineral and/or organic fillers. The choice of fillers may be specific to a particular application and the specific filler incorporated into the chopped strand mat may be chosen to enhance certain properties such as electric resistance and/or conductivity, or biodegradability of the chopped strand mat. The degree of dispersion allows for improved retention of these filler or additives. For example, the closed nature of the dispersed fibers would act as a screen to capture the fillers, and thus, depending on the degree of dispersion, a range of mats could be produced that could include lightly filled mats to highly filled mats with either large or small particle fillers. Such permeability may be used to improve physical properties such as acoustic absorption and surface erosion resistance.

There are numerous advantages provided by the size composition of the present invention. For instance, the polyvinylamine film former may react with the silanes present on the glass surface and with the binder applied on the mat line, in addition to providing bundle integrity during the mat forming process. In doing so, the polyvinylamine film former serves as a chemical link between binder and glass, thereby increasing mat tensile strength. Additionally, the chopped glass fiber bundles can be formed with low manufacturing costs because the wet glass fibers are chopped in-line and are not dried until processed as a glass mat. Also, the increased laminate glass content that is imparted by the chopped strand mats formed with fibers sized with the inventive size composition relative to a traditional wet-laid mat provides improved mechanical and impact performance in the final composite product. Further, it is an advantage of the present invention that the chopped strand mat can be controlled to have a predetermined amount of reinforcement fiber bundles and individual reinforcement fibers to form a mat with a desired weight distribution.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.

EXAMPLES Example 1 Formation of Size Compositions

The sizing formulations set forth in Tables 1-3 were prepared in buckets as described generally below. To prepare the size compositions, approximately 90% of the water and, if present in the size composition, the acid(s) were added to a bucket. The silane coupling agents were added to the bucket and the mixture was agitated for a period of time to permit the silane to hydrolyze. After the hydrolysis of the silane, the polyvinylamine film former was added to the mixture with agitation to form the size composition. The size composition was then diluted with the remaining water to achieve a mix solids|of about 1.5%.

TABLE 1 Low Molecular Weight Polyvinylamine Film Former % Component Solids Fraction Normalized Solids Grams Acetic Acid 100%  0.025 0.025 3.75 3.75 Lupamin 1595^((a)) 10% 0.900 0.900 135.0 1350 A-187^((b)) 71% 0.035 0.035 5.25 7.39 A-1100^((c)) 58% 0.065 0.065 9.75 16.81 DM Water 3622 1.000 1.000 5000 ^((a))a low molecular weight (e.g., 10³-10⁴ g/mol) polyvinylamine film former (commercially available from BASF) ^((b))γ-glycidoxypropyltrimethoxysilane (commercially available from Momentive Materials) ^((c))γ-aminopropyltriethoxysilane (commercially available from Momentive Materials)

TABLE 2 Medium Molecular Weight Polyvinylamine Film Former % Component Solids Fraction Normalized Solids Grams Acetic Acid 100%  0.025 0.025 3.75 3.75 Lupamin 5095^((a)) 10% 0.900 0.900 135.0 1350 A-187^((b)) 71% 0.035 0.035 5.25 7.39 A-1100^((c)) 58% 0.065 0.065 9.75 16.81 Emery 6760L^((d)) 12.5%   0.000 0.000 0.000 0.00 DM Water 3622 1.000 1.000 5000 ^((a))a medium molecular weight (e.g., 10⁴-10⁵ g/mol) polyvinylamine film former (commercially available from BASF) ^((b))γ-glycidoxypropyltrimethoxysilane (commercially available from Momentive Materials) ^((c))γ-aminopropyltriethoxysilane (commercially available from Momentive Materials) ^((d))partially amidated long-chain polyalkylene imine (commercially available from Emery)

TABLE 3 High Molecular Weight Polyvinylamine Film Former % Component Solids Fraction Normalized Solids Grams Acetic Acid 100%  0.025 0.025 3.75 3.75 Lupamin 9095^((a))  7% 0.900 0.900 135.0 1929 A-187^((b)) 71% 0.035 0.035 5.25 7.39 A-1100^((c)) 58% 0.065 0.065 9.75 16.81 Emery 6760L 12.5%   0.000 0.000 0.000 0.00 DM Water 3043 1.000 1.000 5000 ^((a))a high molecular weight (e.g., 10⁵-10⁶ g/mol) polyvinylamine film former (commercially available from BASF) ^((b))γ-glycidoxypropyltrimethoxysilane (commercially available from Momentive Materials) ^((c))γ-aminopropyltriethoxysilane (commercially available from Momentive Materials) ^((d))partially amidated long-chain polyalkylene imine (commercially available from Emery)

Example 2 Formation of Preforms Having Fully Retained Glass Fiber Bundles

Glass fibers sized with the inventive size formulation containing a medium molecular weight polyvinylamine film former were gathered into strands and chopped into chopped glass bundles. The glass fiber bundles were added to a bucket containing a mixture of tap water and a 0.5-1.0% solution of Nalco 7768 (i.e, an anionic polyacrylamide viscosity modifier). The bundled slurry was mixed for approximately 2 minutes and dumped into a deckle box. The preform that was made is photographically depicted in FIG. 3. As can be seen in FIG. 3, the preform had fully retained bundles of fibers.

Example 3 Formation of Preforms Having Partially Dispersed Fiber Bundles

Glass fibers sized with the inventive size formulation containing a medium molecular weight polyvinylamine film former were gathered into strands and chopped into chopped glass bundles. The bundles were added to a bucket containing a mixture of tap water, a 0.5-1.0% solution of an anionic polyacrylamide viscosity modifier (e.g., Nalco 7768), and 100-1000 ppm of an ethoxylated amine (e.g., Nalco 01NM159). The bundled slurry was mixed for approximately 2 minutes and dumped into a deckle box. The preform that was made from the sized glass fibers is photographically depicted in FIG. 4. As can be seen in FIG. 4, the preform contains bundles of fibers and individual fibers dispersed among the fiber bundles. It can be concluded from this experiment and the results obtained from Example 2 where no fibers were dispersed when no ethoxylated amines were present is that the addition of an ethoxylated amine caused fiber dispersion.

Example 4 Molded Preform Laminate Normalized Tensile Strength

Molded preform laminates of wet chop glass fibers and dry chop glass fibers were formed and tested for tensile strength. Unlike the dry chop glass fibers, the wet chop glass fibers were immersed in a bucket containing a mixture of tap water and an anionic polyacrylamide viscosity modifier. The whitewater used to process bundled WUCS 1 and bundled WUCS 2 shown in FIG. 5 is the distinguishing factor between these two samples. Bundled WUCS 2, which had a lower tensile strength than bundled WUCS 1, was formed without an ethoxylated amine in the whitewater. Chopped glass fibers were impregnated with a polyester resin to form the laminated wet chop experimental and dry chop preforms depicted in FIG. 5. It is to be appreciated that the wet chop fibers were dried by conventional methods (such as by a drying oven) to dry the chopped fibers prior to impregnation with the resin. It can be seen in FIG. 5 that both the wet chop and dry chop laminated preforms had similar normalized tensile strengths.

The dry chop glass fibers were formed into a dry chop fiber mat and coated with a conventional binder, as depicted in the far right section of FIG. 5. As shown in FIG. 5, the dry chop fiber mats had significantly higher normalized tensile strengths compared to the mats formed from the wet chop and dry chop fibers. It is to be noted that dry chop fibers do not disperse in whitewater like traditional wet chopped glass fibers (WUCS). Additionally, dry chopped fibers (DUCS) are only slightly sensitive to changes made to the whitewater chemistry in a wet-laid process. Thus, it can be concluded that the dry fibers sized with the inventive composition can be processed like traditional WUCS fibers, and perforn well in applications where dry chopped fibers could be used.

In addition, a preform labeled Exp CSM in FIG. 5 was made using a traditional air-laid process. In particular, dry chopped strands were suspended in air, collected as a loose web on a screen or perforated conveyor, and then consolidated to form a mat of randomly oriented bundles. The preform sized with the inventive sizing composition and the preform formed with the conventional sizing exhibited tensile performances substantially similar to preforms made using a traditional dry chop preform process (i.e., Comparative 1 and Comparative 2). The inventive process in which a polyvinylamine film former is used in the size composition is beneficial because the end product is less costly to manufacture, yet it performs equally well to those preforms formed using conventional processes and size chemistry (i.e., Comparative 1 and Comparative 2). Further, the inventive process produces chopped strand glass mats that have a high glass content, which is often a desired characteristic of fiberglass reinforced panels.

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below. 

1. A sizing composition for reinforcement fibers used in a wet-laid process, said sizing composition comprising: a polyvinylamine film former; and one or more silane coupling agents, wherein said polyvinylamine film former is capable of maintaining the integrity of reinforcement fiber bundles in whitewater or of interacting with components present in said whitewater to at least partially disperse individual reinforcement fibers from said reinforcement fiber bundles.
 2. The sizing composition of claim 1, further comprising a lubricant.
 3. The sizing composition of claim 2, wherein: said polyvinylamine film former is present in said composition in an amount from about 80 to about 95% by weight of the total composition; said one or more silane coupling agents is present in said composition in an amount from about 5.0 to about 20.0% by weight of the total composition; and said lubricant is present in said size composition in an amount up to about 5% by weight of the total composition.
 4. The sizing composition of claim 1, wherein said polyvinylamine film former has a molecular weight in a range from about 10³ g/mol to about 10⁶ g/mol.
 5. The sizing composition of claim 4, wherein said one or more silane coupling agents includes an epoxy silane coupling agent and an aminosilane coupling agent.
 6. The sizing composition of claim 5, wherein said polyvinylamine film former has a molecular weight selected from the group consisting of 10³ to 10⁴ g/mol, 10⁴ to 10⁵ g/mol and 10⁵ to 10⁶ g/mol.
 7. A chopped strand mat formed by a wet-laid process including whitewater for dispersing reinforcing fibers comprising: a plurality of chopped reinforcement fiber bundles formed of a plurality of individual reinforcement fibers at least partially coated with a sizing composition that contains a cationic polyvinylamine film former, wherein said whitewater includes an anionic polyacrylamide thickening agent.
 8. The chopped strand mat of claim 7, further comprising: one or more of said individual reinforcement fibers released from said plurality of chopped reinforcement fiber bundles, wherein said whitewater further includes an amine dispersing agent selected from a cationic amine and a non-ionic amine, and wherein said amine causes the release of said individual reinforcement fibers from said chopped reinforcement fiber bundles.
 9. The chopped strand mat of claim 8, wherein said amine dispersing agent is an ethoxylated amine.
 10. The chopped strand mat of claim 7, wherein said individual reinforcement fibers are glass fibers, and wherein said polyvinylamine film former is cationic and said polyacrylamide thickening agent is anionic, and wherein said cationic polyvinylamine film former and said anionic polyacrylamide thickening agent surround said chopped reinforcement fiber bundles and maintain said chopped reinforcement fiber bundles in a bundled form.
 11. The chopped strand mat of claim 7, wherein said polyvinylamine film former has a molecular weight in a range from about 10³ g/mol to about 10⁶ g/mol.
 12. The chopped strand mat of claim 7, wherein said sizing composition further comprises at least one silane coupling agent and a lubricant.
 13. The chopped strand mat of claim 12, wherein said at least one silane coupling agent comprises an epoxy silane coupling agent and an aminosilane coupling agent.
 14. A wet-laid method of forming a chopped strand mat that includes bundles of reinforcement fibers and a plurality of individual reinforcement fibers comprising the steps of: depositing bundles of reinforcement fibers formed of a plurality of individual reinforcement fibers in whitewater including a polyacrylamide thickening agent and an amine dispersing agent selected from a cationic amine dispersing agent and a non-ionic amine dispersing agent, said plurality of individual reinforcement fibers being at least partially coated with size composition containing a polyvinylamine film former; agitating said whitewater to disperse said bundles of reinforcement fibers and selectively release said individual reinforcement fibers from said bundles of reinforcement fibers; forming a web of said bundles of reinforcement fibers and said individual reinforcement fibers; applying a binder composition to said web; and heating said web to dry said web and cure said binder composition and form a chopped strand mat that includes said bundles of reinforcement fibers and said individual reinforcement fibers, wherein said size composition works with said amine dispersing agent present in said whitewater to selectively disperse said individual reinforcement fibers from said bundles of reinforcement fibers.
 15. The method of claim 14, wherein said size composition further comprises one or more silane coupling agents.
 16. The method of claim 15, wherein said one or more silane coupling agent comprises an epoxy silane coupling agent and an aminosilane coupling agent.
 17. The method of claim 16, wherein said size composition further comprises a lubricant.
 18. The method of claim 14, wherein said amine dispersing agent is an ethoxylated amine.
 19. The method of claim 14, wherein said polyvinylamine film former has a molecular weight in a range from about 10³ g/mol to about 10⁶ g/mol.
 20. The method of claim 14, wherein said individual reinforcement fibers present in said whitewater is controlled by said amine dispersing agent in said whitewater to engineer said chopped strand mat with a predetermined amount of said individual reinforcement fibers. 